The present invention relates generally to continuous process control (CPC) and, more particularly, to dynamically configuring a CPC algorithm.
A commonly used algorithm for continuous process control is known as a “PID” algorithm, where the term “PID” refers to proportional, integral, and derivative. In industrial control systems there are many different types of PID algorithms. The most common types of PID algorithms are either “non-interacting” or “interacting”. With an interacting algorithm, the proportional, integral, and derivative terms are combined in a way in which the terms interact, e.g., the terms are determined in series. With a non-interacting algorithm, the proportional, integral and derivative terms are combined in a way in which the terms do not interact, e.g., the terms are determined in parallel.
Each algorithm type has benefits in different applications and in different control modes. In a control application it may be desirable to iteratively switch back and forth from one control algorithm type to the other control algorithm type in order to heuristically determine the best algorithm for the application. Also over the course of system operation, different control objectives and operating conditions may arise that would make it desirable to switch from one control algorithm type to the other control algorithm type. An example would be a split-range temperature control where the PID output is split into two ranges; one for heating and one for cooling. The desired algorithm type for the heating range may be different from the desired algorithm type for the cooling range. In a continuous process control (CPC) application, stopping the control system to change the control algorithm can cost an inordinate amount of time and money.
In an attempt to avoid such loss of time and money, some CPC algorithms provide for dynamic configuration, which means switching between PID algorithm types without requiring that the control system be stopped. With such dynamic configuration, there can be an abrupt change in the control system algorithm output. Such an abrupt change can cause the controlled process to become unstable, possibly resulting in an emergency shutdown and/or end product degradation.